# Real Time Transfer (RTT)

RuuviTags are nRF52-based devices. The programming is done over Serial Wire Debug (SWD) interface through nRF52 devkit. The RuuviTag can be interfaced to nRF52-DK either through [Ruuvi Devshield](https://shop.ruuvi.com/product/devkit/) or a [Tag-Connect cable](http://www.tag-connect.com/TC2030-CTX-NL).

The Real-Time Transfer is Segger's technology for printing UART-like messages from the attached Cortex-M device. Test versions of Ruuvi Firmware print out the logs via RTT which can be useful for example when developing your own applications which communicate over GATT.

**Connecting the hardware**

First you'll need to connect your PC to nRF52-DK via USB-micro cable, then you'll need to connect the nRF52-DK to Ruuvi via devkit or the Tag-Connect cable. nRF52-DK autodetects an external target and programs it, but if there is an issue with connection you can get errors from the software or program the nRF52 onboard the nRF52-DK. You can cut the power measurement jumper on nRF52-DK to be sure to not accidentally connect to the wrong nRF52.

![RuuviTag zip-tied to devkit with soldered wires for debugging.](/files/-Lt90cJSLERoHKmCbift)

![Programming a RuuviTag with DK and Tag-connect cable](/files/-Lt90rcrkTDkbv7Yd1nm)

If you get a Tag-Connect cable, be sure to get the 10-pin connector Cortex-M no-legs version or you'll need to solder the wires to pins on DK as above.

**Software connection**

You'll need to install[ Segger software and documentation pack](https://www.segger.com/downloads/jlink/). On Windows you can use JLinkRTTViewer which has a GUI for connecting to device and storing the logs to a file, on Linux and Mac OSX you have to use JLinkExe to connect to the Ruuvi and JLinkRTTClient to view the logs.

JLinkExe has to be started first, commands are

* *connect*
* Device -> *NRF52832\_XXAA*
* Interface -> *s* (SWD)
* Speed -> *4000* (kHz)
* Restart program and halt -> *r*
* Once JLinkRTTViewer is connected, go -> *g*

![JLinkExe connected to Ruuvi](/files/-Lt92eIK_ga3Nsut_ODT)

JLinkRTTClient will connect automatically to the JLinkExe session, just start JLinkRTTClient and start the firmware program on JLinkExe with *g.*

![RTT Logs](/files/-Lt92UcUBOH76bV3mJdk)


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